Multi-stage radial turbine

ABSTRACT

A multi-stage radial turbine that is capable of reducing the number of bearings and of improving the conversion efficiency is provided. Provided are a plurality of radial turbine rotor blades ( 5 ) that are attached at intervals to a single rotating shaft ( 3 ); a plurality of nozzles ( 19 ) that are individually installed on an upstream side of each of the radial turbine rotor blades and that accelerate a flow of fluid; a connecting channel portion ( 9 ) that connects gas an outlet portion ( 23 ) of the radial turbine rotor blade ( 5 ) on the front stage side and an upstream side of the nozzle ( 19 ) on the rear stage side, the connecting channel portion ( 9 ) being provided with a U-shaped bent portion ( 25 ) that deflects outward in the radial direction the flow of fluid that is made to flow out from the radial turbine rotor blade ( 5 ) in the shaft direction; a vane portion having a plurality of deflecting vanes ( 27 ) that deflect the flow of fluid inward in a rotation direction (R) while guiding the flow of fluid from the U-shaped bent portion ( 25 ) outward in the radial direction; and a return bent portion ( 31 ) that deflects inward in the radial direction the flow that is made to flow out from the vane portion ( 29 ) while swirling outward in the radial direction.

TECHNICAL FIELD

The present invention relates to a multi-stage radial turbine.

BACKGROUND ART

A radial turbine has a configuration in which a plurality of centrifugalblades are secured to a hub that is secured to a rotating shaft, and airor gas, which is a working fluid that flows inward from an outerperipheral side in the radial direction by using the space betweensubstantially parallel circular plates as a flow channel, acts on thecentrifugal blades, causing the hub to rotate, and flows out insubstantially a shaft direction.

Since it is possible to obtain a high expansion ratio with a singlestage, a radial turbine is generally employed with a single-stageconfiguration.

In order to effectively utilize the energy of a working fluid that showsa large heat drop at a high pressure ratio, it has been proposed toutilize a multi-stage configuration in a radial turbine, that is, toutilize the working fluid in series.

For example, as disclosed in Patent Literature 1, it has been proposedto arrange a plurality of radial turbines in a row, wherein a flow offluid expelled from one radial turbine is introduced into an inlet ofthe next radial turbine to recover the energy of the working fluid. Inthis case, each radial turbine has a shaft with a differing rotationalspeed, and work is performed by using the rotation of the individualshafts.

CITATION LIST Patent Literature

-   {PTL 1} Japanese Unexamined Patent Application, Publication No. Sho    59-79096.

SUMMARY OF INVENTION Technical Problem

With the disclosure in Patent Literature 1, because each radial turbinehas a rotating shaft, the numbers of bearings and shaft seals increase.Because of this, bearing loss and leakage loss increase; therefore, ithas not been possible to efficiently convert the energy of ahigh-pressure working fluid into rotational motive power.

For example, when motive power is supplied for one operation, arotational force is transmitted from the individual output shafts to ashaft for that operation by, for example, employing gears; therefore,there is a problem in that the structure thereof becomes large.

In light of the above-described circumstances, an object of the presentinvention is to provide a multi-stage turbine that is capable ofreducing the number of bearings and of improving conversion efficiency.

Solution to Problem

In order to solve the above-described problems, the present inventionemploys the following solution.

Specifically, an aspect of the present invention is a multi-stage radialturbine including a single rotating shaft; a plurality of radial turbinerotor blades that are attached at intervals to the rotating shaft andthat cause a flow of fluid that flows in from an outer peripheral sidein a radial direction to flow out in substantially a shaft direction; aplurality of nozzles that are individually installed on an upstream sideof each of the radial turbine rotor blades and that accelerate the flowof fluid in a rotation direction; a connecting channel portion thatconnects an outlet portion of the radial turbine rotor blade on a frontstage side and an upstream side of the nozzle on a rear stage side, theconnecting channel portion being provided with a U-shaped bent portionthat deflects outward in the radial direction the flow of fluid that ismade to flow out from the radial turbine rotor blade in the shaftdirection; a vane portion having a plurality of deflecting vanes thatdeflect the flow of fluid in the rotation direction of the radialturbine rotor blades while guiding the flow of fluid from the U-shapedbent portion outward in the radial direction; and a return bent portionthat deflects inward in the radial direction the flow that flows outfrom the vane portion while swirling outward in the radial direction.

With this aspect, the flow of fluid that flows in from the outerperipheral side in the radial direction is accelerated in the rotationdirection by the nozzle and is introduced to the outer peripheralportion of the radial turbine rotor blade. The fluid that has beenintroduced to the radial turbine rotor blade is made to flow out in theshaft direction from the radial turbine rotor blade, passes through theU-shaped bent portion to be deflected outward in the radial direction,and is subsequently deflected in the rotation direction of the radialturbine rotor blade while being guided outward in the radial directionwith the deflecting vanes when passing through the vane portion. Thefluid that is made to flow out from the vane portion while swirlingoutward in the radial direction passes through the return bent portionto be deflected inward in the radial direction and is made to flow intothe nozzle of the next stage from the outer peripheral side in theradial direction. The flow of fluid repeatedly undergoes these processesand is made to flow out in, for example, substantially the shaftdirection from the radial turbine rotor blade of the final stage.Consequently, the rotation of each radial turbine rotor blade istransmitted to the single rotating shaft, and the rotating shaft isrotated.

Since the plurality of radial turbine rotor blades are attached atintervals to the single rotating shaft in this way, bearings and shaftseals need to be provided only for the single rotating shaft, and,naturally, the numbers thereof can be reduced as compared with a case inwhich a plurality of rotating shafts are provided.

Therefore, because the bearing loss and the leakage loss can be reduced,the energy of high-pressure working fluid can be efficiently convertedto a rotational motive force.

Furthermore, the structures of the radial turbine rotor blades and therotating shaft can be made similar to the conventional structures, andit is possible to suppress an increase in the size of the structure ofthe multi-stage radial turbine.

In the above-described aspect, the U-shaped bent portion may beconfigured such that a downstream-portion channel area at an end portioncloser to the vane portion is made smaller than an upstream-portionchannel area at an end portion closer to the radial turbine rotor blade.

Since the U-shaped bent portion is configured in this way such that thedownstream-portion channel area at the end portion closer to the vaneportion is smaller than the upstream-portion channel area at the endportion closer to the radial turbine rotor blade, it is possible toaccelerate the flow of fluid at the U-shaped bent portion.

By doing so, it is possible to suppress flow separation due to theinfluence of the low-flow-speed regions that may occur at the outletportions of the radial turbine rotor blade.

With the above-described configuration, it is preferable that thedownstream-portion channel area be set to be equal to or less than 0.8to 0.9 times the size of the upstream-portion channel area.

The low-flow-speed regions that may occur at the outlet portions of theradial turbine rotor blade generally occupy 10 to 20% of the channelarea at the outlet portions of the radial turbine rotor blade.

With this aspect, because the flow of fluid can be accelerated at theU-shaped bent portion by at least 10 to 20%, it is possible to alleviatethe influence of this low-flow-speed region portion.

In the above-described aspect, it is preferable that the deflectingvanes be configured to form involute curves.

With this configuration, a change between the channel area at the inletportion between the deflecting vanes of the vane portion and the channelarea at the outlet portion thereof can be reduced.

Accordingly, it is possible to reduce the loss due to deceleration, andthe loss due to deflection at the vane portion can be reduced.

Advantageous Effects of Invention

With the present invention, because a plurality of radial turbine rotorblades are attached at intervals to a single rotating shaft, bearingsand shaft seals need to be provided only for a single rotating shaft,and, naturally, the numbers thereof can be reduced as compared with acase in which a plurality of rotating shafts are provided.

Therefore, because bearing loss and leakage loss can be reduced, it ispossible to efficiently convert the energy of a high-pressure workingfluid to rotational motive power.

Furthermore, structures of the radial turbine rotor blades and therotating shaft can be made similar to conventional structures, and anincrease in the size of structures of the multi-stage radial turbine canbe suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial sectional view showing, in outline, theconfiguration of a single-shaft multi-stage radial turbine (multi-stageradial turbine) according an embodiment of the present invention.

FIG. 2 is a sectional view taken along X-X in FIG. 1.

DESCRIPTION OF EMBODIMENTS

A single-shaft multi-stage radial turbine 1 according to an embodimentof the present invention will be described below with reference to FIGS.1 and 2.

FIG. 1 is a partial sectional view, showing, in outline, theconfiguration of the single-shaft multi-stage radial turbine 1. FIG. 2is a sectional view taken along X-X in FIG. 1.

The single-shaft multi-stage radial turbine 1 is provided with arotating shaft 3, a plurality of, for example, two, radial turbine rotorblades 5, a casing 7, and a connecting flow channel portion 9.

The rotating shaft 3 is supported on the casing 7 at one end by a radialbearing (not shown), and the other end thereof is supported by a radialbearing (not shown) and a thrust bearing (not shown).

The plurality of radial turbine rotor blades 5 are attached at intervalsin a shaft direction L of the rotating shaft 3 and make a flow of fluidthat has flowed in from an outer peripheral side in a radial direction Kflow out substantially in the shaft direction L.

The radial turbine rotor blades 5 are provided with hubs 11 that aresecured to the rotating shaft 3, numerous centrifugal blades 13 that aresecured on surfaces of the hubs 11 at equal intervals in thecircumferential direction, and shrouds 15 that are attached at tips ofthe centrifugal blades 13.

In the radial turbine rotor blades 5, gas channels through which gas(working fluid) passes are defined by the hubs 11, the centrifugalblades 13, and the shrouds 15. Portions of the gas channels that arelocated away from the rotating shaft 3 serve as gas inlet portions 21,and portions thereof closer to the rotating shaft 3 serve as gas outletportions (outlet portions) 23.

A doughnut-shaped inlet channel 17 is formed at a portion of the casing7 located on the outer peripheral side of the gas inlet portions 21 inthe radial direction K. The inlet channel 17 is configured so that thegas flows inward in the radial direction K from the outer side of theradial direction K.

An airfoil nozzle 19 that accelerates a gas flow in a rotation directionR is installed on the downstream side of the inlet channel 17, in otherwords, on an upstream side of the radial turbine rotor blade 5.

The connecting channel portion 9 is a channel provided in the casing 7that connect the gas outlet portions 23 of the radial turbine rotorblade 5 on a front-stage side and an upstream side of the nozzle 19 on arear-stage side.

The connecting channel portion 9 is provided with a U-shaped bentportion 25 that deflects a gas flow that has flowed out in the shaftdirection L from the radial turbine rotor blade 5 outward in the radialdirection K, a vane portion 29 that has a plurality of deflecting vanes27 that deflect the gas flow from the U-shaped bent portion 25 in therotation direction R of the radial turbine rotor blades 5, while guidingthe gas flow outward in the radial direction K, and a return bentportion 31 that deflects inward in the radial direction K the gas thatflows out from the vane portion 29 while swirling outward in the radialdirection K.

A downstream-portion channel area A2 at an end portion of the U-shapedbent portion 25 closer to the vane portion 29 is set to have at most 0.8to 0.9 times the area of an upstream-portion channel area A1 at an endportion closer to the radial turbine rotor blade 5. In other words, thedownstream-portion channel area A2 is made smaller than theupstream-portion channel area A1.

This ratio is determined in consideration of low-flow-speed regions Tthat occur at least at the outlet portions of the radial turbine rotorblade 5. The low-speed regions T generally occur so as to occupy 10 to20% of an outlet-portion channel area, that is, the upstream-portionchannel area A1, of the radial turbine rotor blade 5.

Although it is preferable that the downstream-portion channel area A2 besmaller than the upstream-portion channel area A1, it may be madesubstantially equal in size or larger, depending of the usagecircumstances.

As shown in FIG. 2, the deflecting vanes 27 of the vane portions 29 areconfigured so as to form involute curves.

The amount of change between a channel area A3 at an inlet portionbetween the deflecting vanes 27 of the vane portion 29 and a channelarea A4 at an outlet portion thereof can be made considerably smaller ascompared with the amount of change between a channel area A5 at an inletportion between deflecting vanes 33, which linearly expand as shown withtwo-dot chain lines in FIG. 2, and a channel area A6 at an outletportion thereof.

Although it is preferable that the deflecting vanes 27 form the involutecurves, they are not limited thereto, and they may be appropriatelyshaped.

The operation of the single-shaft multi-stage radial turbine 1 accordingto this embodiment, configured as above, will now be described.

A gas flow G1 that is supplied from a gas source (not shown) to theinlet channel 17 of a first stage passes through the inlet channel 17and flows inward in the radial direction K into the nozzle 19 from theouter peripheral side in the radial direction K.

The nozzle 19 accelerates this gas flow G1 in the circumferentialdirection R and supplies it to the gas inlet portions 21 located at anouter peripheral portion of the radial turbine rotor blade 5.

The gas that has been introduced to the radial turbine rotor blade 5 isexpanded when passing through the gas channel defined by the hub 11, thecentrifugal blades 13, and the shroud 15. The centrifugal blades 13 arepushed by means of this expansion and move in the rotation direction R.Since the hub 11 is rotationally moved in the rotation direction R dueto this movement of the centrifugal blades 13, the rotating shaft 3 isrotated.

The gas flow that has flowed out in the shaft direction L from the gasoutlet portions 23 of the radial turbine rotor blade passes through theU-shaped bent portion 25 and is deflected outward in the radialdirection K.

At this time, because the downstream-portion channel area A2 of theU-shaped bent portion 25 is set to be at most 0.8 to 0.9 times the areaof the upstream-portion channel area A1, the gas flow that passesthrough the U-shaped bent portion 25 is accelerated by at least 10 to20%, corresponding to the reduction of the channel area, for example.

Although the low-speed regions T that occupy 10 to 20% of the channelarea generally occur in front of and behind the gas outlet portions 23of the radial turbine rotor blade 5, because at least a correspondinglevel of acceleration occurs at the U-shaped bent portion 25, it ispossible to substantially eliminate the low-speed regions T. In otherwords, the influence of the low-flow-speed regions T can be alleviated.

Because the influence of the low-speed regions T can be alleviated inthis way, by concentrating the low-flow-speed regions T that occur atthe gas outlet portions 23 of the radial turbine rotor blade 5, it ispossible suppress the occurrence of flow separation by means of thecurvature of a surface of the shroud 15 on the downstream side.

Furthermore, in the case in which the downstream-portion channel area A2can be made smaller than 0.8 to 0.9 times the area of theupstream-portion channel area A1, it is possible to further suppressflow separation; therefore, the curvatures of individual portions can bereduced further.

By doing so, the total shaft length of the multi-stage configuration inparticular can be made shorter; therefore, the total length of thesingle-shaft radial turbine 1 can be made shorter, and the single-shaftradial turbine 1 can be made more compact.

When the gas flow subsequently passes through the vane portion 29, it isdeflected in the rotation direction R of the radial turbine rotor blade5 while being guided outward in the radial direction K by the deflectingvanes 27.

At this time, because the deflecting vanes 27 are configured to forminvolute curves, the amount of change between the channel area A3 at theinlet portion between the deflecting vanes 27 and the channel area A4 atthe outlet portion thereof is made small. Accordingly, at the vaneportion 29, it is possible to reduce the loss due to deceleration of thegas flow and the loss due to deflection.

Furthermore, by adjusting the angles of the deflecting vanes 27, a flowangle at the inlet of the nozzle 19 on the downstream side can beadjusted. For example, if the flow angle at the inlet of the nozzle 19is adjusted to be 40 to 50 degrees in the circumferential direction, theinlet-collision loss at the nozzle 19 can be reduced.

The flow that flows out from the vane portion 29 outward in the radialdirection K while swirling passes through the return bent portion 31, isdeflected inward in the radial direction K, and is made to flow into theinlet channel 17 of the next stage from the outer peripheral side in theradial direction K.

A gas flow G2 supplied from the return bent portion 31 passes throughthe inlet channel 17 and flows into the nozzle 19 inward in the radialdirection K from the outer peripheral side in the radial direction K.

The nozzle 19 accelerates this gas flow G2 in the circumferentialdirection R and supplies it to the gas inlet portions 21 located at theouter peripheral portion of the radial turbine rotor blade 5.

The gas that is introduced to the radial turbine rotor blade 5 isexpanded when passing through the gas channel defined by the hub 11, thecentrifugal blades 13, and the shroud 15. The centrifugal blades 13 arepushed by means of this expansion and move in the rotation direction R.Since the hub 11 is rotationally moved in the rotation direction R dueto this movement of the centrifugal blades 13, the rotating shaft 3 isrotated.

The gas flow that has flowed out in the shaft direction L from the gasoutlet portions 23 of the radial turbine rotor blade passes through adischarge channel (not shown) and is discharged to the exterior of thesingle-shaft radial turbine 1.

Since the plurality of radial turbine rotor blades 5 are attached atintervals to the single rotating shaft 3 in this way, bearings and shaftseals need to be provided only for the single rotating shaft 3, and,naturally, the numbers thereof can be reduced as compared with a case inwhich a plurality of rotating shafts are provided.

Therefore, because bearing loss and leakage loss can be reduced, theenergy of high-pressure working fluid can efficiently be converted to arotational motive force. Moreover, the heat drop thereof can beconverted to a rotational motive force with one single-shaft radialturbine.

Furthermore, together with the fact that the structures of the radialturbine rotor blades 5 and the rotating shaft 3 can be made similar tothe conventional structures, it is possible to suppress an increase inthe size of the structures in the single-shaft radial turbine 1.

The present invention is not limited to the above-described embodiment,various modifications may be made within a range that does not departform the spirit of the present invention.

For example, although two stages of the radial turbine rotor blades 5are employed in this embodiment, this may be changed to three stages orgreater. In this case, the radial turbine rotor blades 5 that areadjacent to each other are connected with the connecting channelportions 9.

REFERENCE SIGNS LIST

-   1 single-shaft radial turbine-   3 rotating shaft-   5 radial turbine rotor blade-   9 connecting channel portion-   19 nozzle-   25 U-shaped bent portion-   27 deflection vane-   29 vane portion-   31 return bent portion-   A1 upstream-portion channel area-   A2 downstream-portion channel area-   K radial direction-   L shaft direction-   R rotation direction

1. A multi-stage radial turbine comprising: a single rotating shaft; aplurality of radial turbine rotor blades that are attached at intervalsto the rotating shaft and that cause a flow of fluid that flows in froman outer peripheral side in a radial direction to flow out insubstantially a shaft direction; a plurality of nozzles that areindividually installed on an upstream side of each of the radial turbinerotor blades and that accelerate the flow of fluid in a rotationdirection; a connecting channel portion that connects an outlet portionof the radial turbine rotor blade on a front stage side and an upstreamside of the nozzle on a rear stage side, the connecting channel portionbeing provided with a U-shaped bent portion that deflects outward in theradial direction the flow of fluid that is made to flow out from theradial turbine rotor blade in the shaft direction; a vane portion havinga plurality of deflecting vanes that deflect the flow of fluid in therotation direction of the radial turbine rotor blades while guiding theflow of fluid from the U-shaped bent portion outward in the radialdirection; and a return bent portion that deflects inward in the radialdirection the flow that flows out from the vane portion while swirlingoutward in the radial direction.
 2. A multi-stage radial turbineaccording to claim 1, wherein the U-shaped bent portion is configuredsuch that a downstream-portion channel area at an end portion closer tothe vane portion is made smaller than an upstream-portion channel areaat an end portion closer to the radial turbine rotor blade.
 3. Amulti-stage turbine according to claim 2, wherein the downstream-portionchannel area is set to be equal to or less than 0.8 to 0.9 times thesize of the upstream-portion channel area.
 4. A multi-stage radialturbine according to claim 1, wherein the deflecting vanes areconfigured to form involute curves.
 5. A multi-stage radial turbineaccording to claim 2, wherein the deflecting vanes are configured toform involute curves.
 6. A multi-stage radial turbine according to claim3, wherein the deflecting vanes are configured to form involute curves.